The error-related negativity (ERN) is an electrocortical response observed at the scalp that is maximal approximately 50 ms after an erroneous response. A number of studies have reported increased ERNs in anxious and depressed participants, and recently, a similar pattern of results has been reported in anxious pediatric patients both before and after successful therapy. Other studies have reported increased error- related brain activity in subjects who report high levels of negative emotionality and punishment sensitivity personality traits that are elevated across both anxiety disorders and depression. Collectively, these results suggest that an increased ERN may reflect information-processing abnormalities during self-monitoring that reflect a shared risk factor for anxiety and depressive disorders. To address this possibility, the present study will examine the ERN in relation to two well-known risk factors related to the development of anxiety and depressive disorders: familial psychopathology and temperamental measures of negative emotionality and behavioral inhibition. The overall goal of this study is to evaluate the relationship between error-related brain activity and the development of anxiety and depression, and to assess the utility of error-related brain activity as a potential endophenotype for affective psychopathologies. Additionally, the present study will contribute to the literature on the developmental neurobiology of individual differences in temperament and personality. PUBLIC HEALTH RELEVANCE: This study explores the relationship between error-related brain activity, and parental psychopathology and laboratory measures of behavioral inhibition and negative emotionality in a sample of 300 6-year olds. The present study aims to examine whether variation in error- related brain activity relates to these well-known risk factors for developing both anxiety and depressive disorders.